(1) Field of the Invention
The present invention relates to an antivibration suspension system for a tie bar of a power transmission gearbox, to an antivibration suspension structure having the antivibration suspension system, and to an aircraft having such a structure.
The invention thus lies in the narrow technical field of devices for reducing vibration on board aircraft.
(2) Description of Related Art
Among aircraft, rotorcraft have at least one lift rotor associated with a carrier structure, which carrier structure is usually referred to as an “airframe” or a “fuselage”.
Such an aircraft also has a power plant for driving a power transmission gearbox that is secured to the carrier structure of the aircraft. The power transmission gearbox then includes a mast for driving the lift rotor in rotation.
The power transmission gearbox is often connected to the carrier structure via its bottom wall and via associated fastener means generally comprising three or four sloping or vertical bars. Such a bar is referred to more simply below as a “tie bar”. Because of its shape, the mounting structure for the lift rotor, i.e. the structure comprising the power transmission gearbox and the tie bars is sometimes referred to by the person skilled in the art as a “pylon”.
The lift rotor and/or the power transmission gearbox can give rise to vibration that can degrade the comfort of occupants of the aircraft by generating vibratory motion and noise in the aircraft. Furthermore, equipment of the aircraft arranged in the carrier structure runs the risk of being degraded by the vibration generated by the mechanical assembly comprising the power transmission gearbox and the lift rotor.
Under such circumstances, various antivibration suspension structures are used at least to reduce vibration within the aircraft, and in particular within a cabin for the comfort of pilots and passengers.
Such an antivibration suspension structure must be capable firstly of transmitting the static loads induced by the mechanical assembly, and secondly of filtering the vibration induced by the mechanical assembly. A manufacturer generally seeks to obtain an antivibration suspension structure that has minimum impact in terms of weight and cost.
In the state of the art, antivibration suspension systems comprise resonators. The effects of resonators is to smother given vibration by creating vibration in phase opposition relative to the given vibration.
Such a resonator for a power transmission gearbox is sometimes provided with a lever supporting a fly-weight for each tie bar. Each sloping tie bar is thus hinged to a carrier structure by a lever supporting a fly-weight. Each lever is then hinged to the carrier structure via a torsion spring.
Each lever may possibly co-operate with a torsion spring or a torsion tube.
By way of example, Document FR 2 982 583 describes an antivibration suspension system comprising a lever extending from a distal end supporting at least one fly-weight to a proximal end provided with a first hinge for hinging the lever to the carrier structure. The antivibration suspension system has a second hinge for hinging the lever to a tie bar of a power transmission gearbox. Torsion return means are provided with a rotary actuator for adjusting the stiffness in twisting of the lever as a function of the flight conditions of the aircraft.
Those antivibration suspension structures provided with a lever carrying a fly-weight are advantageous. When the tie bar is excited by vibration, the tie bar in turn excites the lever. The fly-weight then performs swinging motion that serves to generate vibration that is in phase opposition relative to the original vibration.
Nevertheless, the lever presents a length that is relatively long considerably amplifying the swinging needed of the fly-weight. Such a length for the lever can make installing the antivibration suspension structure difficult in a congested environment.
Document FR 2 878 594 describes a device having at least one resilient plate. At least one resonator has two laminated elastomer bearings, each fastened to the resilient plate.
Document U.S. Pat. No. 4,365,770 describes a device having two masses. The two masses are carried by suspension arms. In addition, a spring extends from one mass to the other mass.
Document EP 0 853 197 does not form part of the technical field of the invention since it concerns a wind turbine. By way of information, Document EP 0 853 197 presents a resonator having two mutually meshing masses. The two masses drive an aluminum disk that carries a permanent magnet in order to generate an eddy current.
Documents FR 2 787 762, GB 207028, U.S. Pat. No. 1,641,230, and U.S. Pat. No. 6,016,289 are also known.